whoa buddy let's not get exaggerated here. "easily" be the champ in the UFC... at MW, LHW and be a top contender at HW? LOL. i'm not saying he couldn't do one of those things, but let's not get ahead of ourselves and say he could do all those things "easily". that's speculating way too much.

mousasi has some good wins under his belt but has he ever faced anderson silva? no. lyoto machida? no. lesnar? no. i think he is a bit afraid to come to UFC. it's a whole different world here with much better fighters than who he has been fighting. he beat babalu, but babalu was never great in UFC, and got kicked out. he beat kang, but kang came to UFC and has looked less than stellar so far. he beat manhoef, but that's essentially beating a K-1 fighter with BJJ because manhoef has less than 0 ground skills. mousasi will probably beat soku but soku couldn't hang in the UFC and got released. the top fighters in UFC are much better in every aspect than the opponents he has been beating.
anyways, my point is, he would not "easily" become champ of anything in UFC, let alone MW, LHW and be a top contender in HW.